Detergent compositions are improved in handling characteristics by allowing them to have a proper viscosity corresponding to each use or made to have a system increased appropriately in viscosity to keep the dispersibility of water-insoluble substances compounded therein.
Generally, alkanolamide type surfactants, betaine type surfactants and semi-polar type surfactants (e.g., alkyldimethylamine oxides) are known as thickeners and used in many surfactant applications at present.
The alkanolamide type surfactants are classified into a monoalkanolamide type and a dialkanolamide type. Although the monoalkanolamide type has a high thickening effect, it cannot be said to be a compound having high handling characteristics because it has a high melting point.
On the other hand, the dialkanolamide type has excellent compounding stability. However, this type is inferior in thickening effect to the monoalkanolamide type and it is therefore difficult to obtain a desired viscosity in a reasonable amount.
In this situation, a thickener which has high compounding stability, a high thickening effect, is superior in foaming characteristics and is preferably used for detergent compositions and the like has been desired.
In the meantime, JP-A No. 11-246500 discloses a method of producing an amide compound represented by the formula (I′) and that this amide compound has high performance as a surfactant. 
In the formula, R11 represents a straight-chain or branched alkyl or alkenyl group having 7 to 21 carbon atoms, R12 represents a straight-chain or branched alkyl or alkenyl group having 1 to 4 carbon atoms and R13 represents a hydrogen atom, a straight-chain or branched alkyl or alkenyl group having 1 to 21 carbon atoms, a straight-chain or branched alkyl or alkenyl group having 1 to 21 carbon atoms, containing two or less hydroxy groups or alkoxyl groups and excluding groups represented by —CH2CH(OH)CH2OR12 or a group represented by -(A′O)n—H (where A′ represents an ethylene group or a propylene group and n denotes a number of 1 to 10).
However, this reference only discloses that the amide compound is useful as a foam-increasing agent. Also, the amide compounds disclosed specifically in the examples described in this reference are all tertiary amide compounds and therefore essentially differ from the fatty acid amide ether compound according to the present invention.